Photographic emulsion containing copper halide host crystals

ABSTRACT

A photographic emulsion containing composite crystals of (a) silver halide and (b) copper halide or a solid solution crystal of copper halide and silver halide is found to be sufficiently photosensitive and developable. In such a photographic emulsion, the amount of silver used can significantly be decreased.

This invention relates to a novel photographic emulsion. Moreparticularly, the present invention pertains to a photographic emulsion,comprising a copper halide crystal in combination with a silver halidecrystal, which is sufficiently photosensitive and developable with arelatively decreased amount of silver halide in the emulsion, thusenabling significant saving of silver metal in photographic technology.

Silver metal, which has been used as starting material for silver halidein photographic emulsions, suffers from scarcity in natural resources.Hence it is very expensive and techniques for saving consumption ofsilver are earnestly desired.

An object of the present invention is to provide a novel photographicemulsion useful for production of a photographic emulsion in which theamount of silver used can be saved.

Another object of the present invention is to provide a photographicemulsion in which the amount of silver used is saved by use of the novelphotographic emulsion.

Still another object of the present invention is to provide a method forpreparation of a novel photographic emulsion in which the amount ofsilver used can be saved.

Other objects of the present invention will become apparent as thedescription proceeds hereinafter.

The objects of the present invention can be achieved by a photographicemulsion, comprising composite crystals composed of (a) silver halide,and (b) copper halide or solid solution crystal of copper halide andsilver halide.

According to a preferred embodiment of the present invention, there isprovided a photographic emulsion, wherein the composite crystalcomprises a copper halide crystal or a solid solution crystal of acopper halide and a silver halide as host crystal and a silver halidecrystal which is epitaxially junctioned onto said host crystal.

I. HOST CRYSTAL

The host crystal useable for the present invention is a copper halide ora solid solution crystal of a copper halide and a silver halide. Thehost crystals are multifaceted radiation-sensitive crystals, having amean granular diameter of at least 0.05μ, preferably 0.1 to 5μ, havingpreferably substantially the zincblende type crystalline structure.

The photographic emulsion comprising copper halide crystals or silverhalide-copper halide solid solution crystals according to the presentinvention (hereinafter referred to as Emulsion A) can be preparedaccording to the conventional method for preparation of silver halideemulsions by simultaneous mixing, wherein mixing and physical ripeningare effected at a P[X] value (wherein [X] represents halogen ionconcentration) maintained at 1 to 6.

The Emulsion A can be prepared by, for example, mixing a solutioncontaining copper nitrate (or further silver nitrate about one mole astotal amount/liter) with a solution containing potassium halide (aboutone mole/liter), sodium sulfite (10⁻⁴ to 1 mole/liter) and about 0.1 to5% by weight of gelatin as protective colloid by a simultaneous mixing,wherein the halogen of potassium halide is chlorine, bromine, iodine, ora mixture thereof. The obtained crystal is proved to have substantiallysingle crystal structure by means of X-ray diffraction analysis.

In the Emulsion A, there is employed a hydrophilic colloid as protectivecolloid or binder. Typical examples of the hydrophilic colloid are thoseconventionally used in the preparation of silver halide emulsions, i.e.natural materials such as gelatin, gelatin derivatives orpolysaccharides, synthetic polymers such as water-soluble polyvinylcompounds, etc.

The Emulsion A is used for preparation of a photographic emulsioncomprising composite crystals as hereinafter described.

II. COMPOSITE CRYSTALS

According to one embodiment of the present invention, the photographicemulsion contains composite crystals of the host crystal andsubstantially silver halide crystal, which are combined through ahetero-junction, typically epitaxial junction. In the epitaxiallyjunctioned composite crystals containing copper halide and silver halideaccording to the present invention, the host crystal, which may becopper halide crystal or a solid solution of copper halide and silverhalide, is combined with a silver halide such as silver chloride, silverbromide, silver chlorobromide, silver iodobromide, silverchloroiodobromide or the like through an epitaxial junction. Preferably,the composite crystal comprises host crystals having substantially thezincblende type crystalline structure, and, epitaxially junctioned onsaid host crystal, crystals substantially consisting of silver halidehaving substantially the sodium chloride type crystalline structure.

In the present specification, the term "epitaxy" is used to signify thesame meaning as described in U.S. Pat. No. 4,094,684 (hereinafterreferred to as Reference 1) and U.S. Pat. No. 4,142,900 (hereinafterreferred to as Reference 2). Namely, the term "epitaxy" means thecrystal orientation of silver halide atoms which is deposited on a hostcrystal grown under the influence of the host crystal.

The content of the epitaxially junctioned silver halide crystal in thecomposite crystal is not more than 75 mol %, preferably not more than 50mol %, based on the total copper halide and silver halide of thecomposite crystal.

One of the main characteristics of the present invention lies in thatthe host crystals are the multi-faceted crystals containing copperhalide. Another main characteristic lies in the epitaxial junction ofsilver halide crystal to the above-mentioned host crystals. Theemployment of the host crystals containing copper halide and epitaxialjunction of silver halide thereto can bring about a decrease in amountof the silver required and can also increase the photosensitivity.

The formation of the composite crystals can be done, for instance, bythe following processes.

(A) A solution containing a water-soluble halide and a silver saltsolution are simultaneously added to the host crystals so that crystalsof silver chloride, silver chlorobromide, silver iodobromide, silverchloroiodobromide or the like are deposited through the epitaxialjunction.

(B) Crystals of silver chlorobromide, silver chloroiodobromide, silveriodobromide or the like are deposited on the host crystals throughepitaxial junction by applying the conversion method stated in, forexample, Reference 2.

(C) A solution containing a water-soluble chloride, bromide and/oriodide is added to an emulsion containing the host crystals,water-soluble silver salt and a protective colloid by the single jetmethod to deposit crystals of silver chloride, silver bromide, silverchlorobromide, silver iodobromide, silver chloroiodobromide or the likethrough the epitaxial junction.

(D) A solution containing a water-soluble silver salt is added to anemulsion containing the host crystal, a water-soluble halide and aprotective colloid by the single jet method to deposit a crystal such assilver chloride, silver bromide, silver chlorobromide, silveriodobromide, silver chloroiodobromide through the epitaxial junction.

The photographic emulsion having the composite crystal of the inventioncan be coated and dried on an appropriate support to prepare a silverhalide emulsion layer, exposed imagewise by an actinic ray and developedunder an appropriate developing condition to yield a photographic silverimage.

The photographic emulsion having the composite crystal of the presentinvention shows preferred interimage and edge effects. The host crystalsconsisting of copper halide or silver halide-copper halide solidsolution have a sensitivity not lower than that of the silver iodidecrystals disclosed in References 1 and 2. The second portion of each ofthe composite crystals, that is a portion formed on the host crystal ofthe above solid solution through epitaxial junction, consistssubstantially of a silver halide crystal. The term "substantially"herein mentioned means that there may also be contained other atoms thanthese silver halides, as far as they do not impair the characteristicsof the photographic emulsion. As such other atoms, there may be includedthe copper atoms to be incorporated into the epitaxial crystal from thehost crystal during preparation steps.

In the epitaxial composite crystals, the host crystal serves as aradiation-receptor. If the photographic emulsion containing compositecrystals of the present invention are exposed imagewise to UV or a bluelight, a developable latent image is formed. If the epitaxial compositecrystals are exposed, the epitaxial silver halide crystal portions aremade developable.

The host crystal in the composite crystal of the present invention hasoptimum amount and composition which are to be determined depending onthe uses of the photographic emulsion having the composite crystal. Forexample, when it is desired to save the amount of silver to be used,there may be employed a copper halide crystal of a solid solutioncrystal containing not less than 80 mol % of copper halide based ontotal silver halide and copper halide of the host crystal. On the otherhand, when a high photosensitivity is necessary, there may be employed asolid solution crystal containing 1 to 80 mol % of copper halide basedon total silver halide and copper halide of the host crystal. Whenchlorine or bromine atoms are contained in a host solid solution crystalas the silver halide or copper halide, copper halide of the host crystalis preferably more than 70 mol % based on the total host crystal.

In the host crystal, the copper halide and silver halide preferably havea common halide component, e.g. copper chloride and silver chloride;copper chlorobromide and silver chlorobromide; etc.

Photosensitivity of the solid solution crystal containing copper iodideand silver iodide, which is in the form of thin film prepared byevaporation, may be attributable to the capacity of said solid solutionabsorbing radiations with longer wavelengths as compared with silveriodide, as disclosed in Phys. Rev. 129(1), (1963), p.69-78, by M.Cardona.

The epitaxial silver halide portion of the composite crystal does notserve as the radiation receptor in the composite crystal. Accordingly,the photographic speed of the photographic emulsion of the presentinvention is not predominently controlled by radiation given to theepitaxial silver halide.

The optimum amount and composition of the epitaxial silver halide usedfor the present invention can be selected according to the purpose ofthe photographic emulsion of the present invention. For instance, ifcharacteristics in which the exposure level to radiation is high and thedeveloping speed is high are required, the epitaxial silver halide at ahigher ratio is employed, as compared with a case in which lowerexposure level to radiation and lower developing speed are required. Ifan improvement on the storage stability of the composite silver halideemulsion is particularly intended, epitaxial silver halide containingsilver bromide or silver iodide is employed. If the emulsion is to besubjected to a combined developing, bleaching and fixing treatment, anepitaxial silver halide composition is optionally selected so that thebalance among the developing speed, the bleaching speed and the fixingspeed can be advantageously controlled.

The epitaxial silver halide crystal employed for the present inventionmakes the composite crystals reactive to the surface development.Namely, the photographic emulsion of the present invention can bedeveloped in a surface developing solution after imagewise exposure. Thesurface developing solution contains substantially no soluble iodidesalt and silver halide solvent, and can initiate development of a latentimage being present on the facet of the silver halide crystal.

Preferable epitaxial silver halide of the composite crystal depositedonto the host crystal is AgCl, AgBr, AgClBr or AgClBrI (I<7 mol %). Thehost crystal and the epitaxial crystal have preferable common halidecomponent, e.g. CuCl/AgCl, CuAgCl/AgCl, CuBr/AgBr, CuClBrI/AgClBrI,CuAgBrI/AgBrI, etc. Practically, important combinations of the hostcrystal and the epitaxial crystal are CuCl/AgCl, CuBr/AgBr,CuClBr/AgClBr, CuI/AgClBr and CuI/AgClBrI.

The composite crystals employed for the present invention can be soformed that a latent image can be made present inside of the crystalstructure rather than present on the crystal structure facets uponexposure. In other words, the epitaxial composite silver halide crystalsincluded in the present invention can be so formed as to become crystalsfor forming an internal latent image predominantly. To predispose thecomposite crystals form an internal latent image, an internal dopant canbe incorporated into the epitaxial silver halide crystal. Examples ofthe internal dopant include silver, sulfur, iridium, gold, platinum,osmium, rhodium, tellurium, selenium, etc. The photographic emulsioncontaining the composite crystals according to the present invention canbe developed, for instance, with an internal developing solutioncontaining a silver halide solvent or a soluble iodide. When thecomposite crystals for forming predominently an internal latent imageare prepared, the epitaxial silver halide crystals are formed in thepresence of, for instance, a non-silver metal ion, preferably apolyvalent metal ion. The epitaxial silver halide crystals arepreferably formed in the presence of the water-soluble salts of therespective metal, most preferably in an acidic medium. Preferredexamples of the polyvalent metal ions include divalent metal ions suchas lead ions, trivalent metal ions such as antimony, bismuth, arsenic,gold, iridium, rhodium and the like and tetravalent metal ions such asiridium and the like. Particularly preferred polyvalent metal ions to beemployed are iridium, bismuth and lead ions. The epitaxial silver halidecrystals generally contain at least 10⁻⁹ mole %, preferably at least10⁻⁶ mole % of the internal dopant based on the epitaxial silver halide.The dopants are generally present in the epitaxial silver halide grainin a concentration of less than about 10⁻¹ mole, preferably 10⁻⁴ mole,per mole of epitaxial silver halide.

The composite crystals employed for the present invention can beprepared by depositing epitaxial silver halide crystal on facets ofcopper halide crystals or silver halide-copper halide solid solutioncrystals serving as the host crystals, for instance, in one of themethods (A), (B), (C) and (D) described hereinbefore. Preparation ofsilver halide-copper halide solid solution crystal is also possibleaccording to the methods as shown in Examples 2 and 3 shown below inaddition to the foregoing methods.

The photographic silver halide emulsion of the present invention can beblended with other emulsions so as to obtain specified photographiccharacteristics. This procedure enables control of both photographicsensitivity and contrast. If the photographic silver halide emulsion ofthe present invention comprises the composite crystals specified by thepresent invention and other silver halide crystals blended therewith andif the composite crystals occupy at least 50% by weight of the totalsilver halide crystals, the composite crystals mainly participate in theformation of image. Even though the amount of the composite crystals isless than 50% by weight, the interimage effect and edge effect can beeffectively controlled.

In the present invention, the composite crystals specified by thepresent invention can be blended with silver chloride crystals. Anadvantageous aspect of the incorporation of silver chloride crystalslies in that the developing speed and/or the silver image density can besubstantially enhanced due to the physical development of the silverchloride crystals, even though the silver chloride crystals are notdeveloped chemically or directly under the conditions specified forexposure and development. The ratio for blending the composite silverhalide crystals specified by the present invention with the silverchloride crystals can be optionally selected depending upon the purpose.If a prominent effect is desired to be achieved in the solution physicaldevelopment, 1-50% by weight, particularly 5-50% by weight, of the totalsilver halide content is preferably occupied by the silver chlorideblended with the composite crystals specified by the present invention.

As the protective colloid or binder to be used in the composite crystalphotographic emulsion according to the present invention, there may beused those conventionally used in silver halide emulsions.

A photographic emulsion of the present invention can be coated on anappropriate support to provide a photographic silver halidephotosensitive material. Into a photographic emulsion of the presentinvention or a photographic photosensitive material, a variety ofphotographic additives can be incorporated in the manners described inReferences 1 and 2. There can be incorporated, for instance, asensitizing dye, coupler, development controlling agent, antifoggant,stabilizer, developing agent, film hardening agent, antistatic agent,plasticizer, lubricating agent, bleaching agent, ultra violet absorber,antihalation dye, and filter dye, as desired.

A photographic emulsion of the present invention is advantageouslyapplied to a variety of light-sensitive silver halide photographicmaterials such as those for X-ray, color, black-and-white, transferprocess, high contrast photography and photothermography.

The photographic emulsion of the present invention can be chemicallysensitized in a conventional manner. Applicable chemical sensitizingagents and examples of preferred sensitizing processes are described inResearch Disclosure No. 176, 17643 page 22-33 (hereinafter referred toas Reference 3). The photographic emulsion of the present invention canbe spectrally sensitized by applying a sensitizing dye which is used inthe conventional silver halide emulsion.

Further, examples of development processes for a photographicphotosensitive material employing the photographic emulsion of thepresent invention are described in Reference 3. For instance, thelight-sensitive silver halide photographic material can be processedthrough a conventional physical development process or can be subjectedto a transfer process generally employed, such as the colloid transferprocess, silver salt diffusion transfer process, inhibition transferprocess, color transfer process, etc.

The photographic emulsion of the present invention is advantageouslyapplicable to a redox amplification process requiring a heterogeneouscatalyst for enabling the reaction between an oxidizing agent and areducing agent. Examples of the oxidizing agent and reducing agent andconcrete procedures are described in References 1 and 2. Thephotographic emulsion of the present invention can be applied to athermosensitive light-sensitive photographic material, as described inthese References.

The conventional process such as bleaching, bleach-fixing, fixing orwater-washing may also be employed for the photographic material usingemulsion of the present invention in the same way as the conventionalsilver halide photographic material.

As described above, the photographic emulsion of the present inventionmay be formulated into a composite crystal photographic emulsion inwhich the solid solution crystal is combined through the epitaxialjunction with silver halide. With such a constitution, the amount ofsilver used can advantageously be decreased with increasedphotosensitivity, as compared with a well-known silver halide emulsioncomprising the composite silver halide crystals having silver halideepitaxially junction onto a part of the facets of multi-faceted crystalsof silver iodide.

The present invention is further illustrated by the following examples,but these examples should not be construed to limit the presentinvention.

EXAMPLE 1

A monodispersed silver iodide emulsion was prepared employing the threesolutions set forth in Table 1.

                  TABLE 1                                                         ______________________________________                                        Solution A                                                                              Ossein gelatin      100.0  g.                                                 Distilled water     3.0    l.                                                 KI                  2.23   g.                                                 Temperature         35°                                                                           C.                                                 pH                  6.0                                             Solution B                                                                              5 molar aqueous solution of KI                                                                    1,000  ml.                                      Solution C                                                                              5 molar aqueous solution of                                                                       800    ml.                                                AgNO.sub.3                                                          ______________________________________                                    

An iodine ion electrode and a double-junction type silver/silverchloride reference electrode (junction solution: 1 molar KNO₃ aqueoussolution) sold on the market were immersed in Solution A to measure thepotential. The potential (-175 mV) was maintained during addition ofSolutions B and C by adjusting the flow rate of Solution B.

Solution C was added at a constant flow rate of 0.5 ml./min. during theinitial 6 min. period, and subsequently the flow rate was elevatedstraight forwardly by a rate of 0.385 ml./min. per every 10 min. Thecomplete addition of Solution C required 197 min., and the temperatureof the solution was kept at 35° C. during the physical aging procedure.When the addition of Solution C was complete, the addition wasdiscontinued. Subsequently, washing with water and desalting werecarried out in the following manner.

A precipitant [5% aqueous solution of Demol N® (polymethylenebis-sodiumnaphthalene sulfonate), produced by Kao Atlas Co., Ltd., Japan] and anaqueous solution of magnesium sulphate (20%) were added in a ratio of10:9 until a precipitate was produced. The precipitate was allowed tostand quietly to form a sediment, and then the supernatant liquid wasremoved by decantation. To the sedimented precipitate was added 3,000ml. of distilled water to disperse again the precipitate. An aqueoussolution of magnesium sulfate (20%) was further added to the so obtaineddisperse system until a precipitate was again produced. Aftersedimentation of the precipitate was complete, the supernatant liquidwas removed by decantation. The aqueous solution of ossein gelatincontaining 56.6 g. of gelatin was added to the precipitate, and theprecipitate was dispersed under stirring at 35° C. for 20 min. Then,distilled water was so added to the disperse system to make the totalvolume to be 2,270 ml. The so obtained emulsion is referred tohereinafter as EM-1. The mean diameter of the grains contained in theEM-1 emulsion and the standard deviation of the granular diameter wereconfirmed to be 0.25 μm and 20% of the mean granular diameterrespectively upon observation of the electron microscope photograph.Moreover, the X-ray diffraction analysis indicated that the EM-1emulsion consisted substantially of β-phase silver iodide with littleamounts of those of α- and γ-phases.

EXAMPLE 2

An emulsion comprising fine AgCuI crystals containing 15 mole % of CuIwas prepared employing the three solutions set forth in Table 2.

                  TABLE 2                                                         ______________________________________                                        Solution D:                                                                             Ossein gelatin     30     g.                                                  Na.sub.2 SO.sub.3  120    g.                                                  KI                 19.8   g.                                                  Distilled water    3,000  ml.                                                 Ethanolic aqueous solution                                                    of sodium salt of polyiso-                                                    propylene-polyethylenoxy-                                                     disuccinate (10%)  1.5    ml.                                       Solution E:                                                                             AgNO.sub.3         144.4  g.                                                  Cu(NO.sub.3).sub.2 3H.sub.2 O                                                                    34.5   g.                                                  Water added to make up                                                                           1,000  ml.                                       Solution F:                                                                             KI                 166    g.                                                  Ossein gelatin     20     g.                                                  Water added to make up                                                                           1,000  ml.                                       ______________________________________                                    

An iodide ion electrode and a double-junction type saturatedsilver/silver chloride reference electrode (junction solution: 1 molarKNO₃ aqueous solution) sold on the market were immersed in Solution D tomeasure the potential. Solutions E and F were added to Solution D underadjustment of a flow rate of Solution E to maintain the potentialconstantly at -190 mV during the addition of Solutions E and F. The rateof addition of Solution E was controlled constantly at 3.13 ml./min. forone to two minutes from the beginning of the addition, thereafterincreased linearly at the rate of 2.41 ml./min. per two minutes. It took40 minutes before all of Solution E was added. Washing with water anddesalting were conducted similarly as in Example 1, followed byre-dispersion in a gelatin solution. This emulsion is hereinafterreferred to as EM-2.

EXAMPLE 3

Using the three solutions set forth in Table 3, there was prepared anemulsion in which pure silver chloride was epitaxially grown on silveriodide as prepared in Example 1.

                  TABLE 3                                                         ______________________________________                                        Solution G:                                                                             Ossein gelatin       4.4    g.                                                KCl                  1.0    g.                                                Em-1 emulsion        160    ml.                                               Distilled water      840    ml.                                     Solution H:                                                                             One molar AgNO.sub.3 aqueous                                                  solution                                                            Solution I:                                                                             One molar KCl aqueous solution                                      ______________________________________                                    

There were added 70.6 ml. of Solution H and 70.6 ml. of Solution I toSolution G at 35° C. simultaneously over 6 minutes according to thedouble-jet method. After completion of the addition, washing with waterand desalting were conducted according to the following procedure. Aprecipitant (5% aqueous solution of Demol N, produced by Kao Atlas Co.,Ltd., Japan) and an aqueous solution of magnesium sulphate (20%) wereadded in a ratio of 10:9 until a precipitate was produced. Theprecipitate was allowed to stand quietly to form a sediment, and thenthe supernatant liquid was removed by decantation. To the sedimentedprecipitate was added 800 ml. of distilled water to disperse again theprecipitate. An aqueous solution of magnesium sulfate (20%) was furtheradded to the so obtained disperse system until a precipitate was againproduced. After sedimentation of the precipitate was complete, thesupernatant liquid was removed by decantation. The aqueous solution ofossein gelatin containing 10 g. of gelatin was added to the precipitate,and the precipitate was dispersed under stirring at 35° C. for 20minutes. Then distilled water was added to the disperse system to make atotal volume to 200 ml. The so obtained emulsion is hereinafter referredto as EM-3.

EXAMPLE 4

According to the method similar to Example 3, by replacing EM-1 inSolution G in Table 3 with EM-2, there was prepared an emulsion in whichAgCl was epitaxially junctioned on AgCuI. The so obtained emulsion ishereinafter referred to as EM-4.

EXAMPLE 5

The emulsions EM-1 and EM-2 which had not yet been chemically sensitizedwere coated on film supports, respectively, in the amounts of gelatin of4.00 g/m² and the sum of silver and copper of 0.046 mol/m² (Sample Nos.1 and 2). These samples were exposed to white light through an opticalwedge in a KS-1 type Sensitometer (manufactured by Konishiroku Photo.Ind. Co., Ltd., Japan), and then treated in the developing solutionhaving the following composition at 20° C. for 10 minutes, followed byfixation treatment and washing with water.

    ______________________________________                                        Developing solution                                                           ______________________________________                                        Metol                  6      g.                                              Sodium sulfite (anhydrous)                                                                           50     g.                                              Hydroquinone           6      g.                                              Sodium carbonate       29.5   g.                                              Potassium bromide      1.0    g.                                              Add water to make      1      liter                                           ______________________________________                                    

The results obtained upon sensitometry are set forth in Table 4.

                  TABLE 4                                                         ______________________________________                                        Sample            Relative                                                    No.      EM No.   sensitivity  D.sub.min.                                                                         D.sub.max.                                ______________________________________                                        1        1        No           0.03 0.08                                      2        2        No           0.03 0.08                                      ______________________________________                                         Note:-                                                                        Relative sensitivity was determined at D.sub. min. + 0.10. No means that      the determination was not possible.                                      

As seen from the results shown in Table 4, EM-2 and EM-1 show extremelylow photographic reactions.

EXAMPLE 6

To each of the silver halide emulsions of EM-3 and EM-4 was added2.0×10⁻⁵ mole of sodium thiosulfate and 1.0×10⁻⁵ mole of sodiumchloroaurate per mole of each emulsion, and the mixture was stirred at45° C. for 60 minutes. Subsequently, to the resulting mixture were added4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene and1-phenyl-5-mercaptotetrazole, and bis(vinylsulfonylmethyl) ether andsaponin were further added thereto just prior to being coated. Themixture was then coated on a support in amounts of 0.028 mole/m² and 2.0g/m² of gelatin to prepare samples (Sample Nos. 4 and 5). The amount ofthe coating was adjusted so that the total moles of silver halide andcopper halide may be equal per unit area. These samples were exposed towhite light through an optical wedge in a KS-1 type Sensitometer(manufactured by Konishiroku Photo. Ind. Co., Ltd., Japan), and thensubjected to the treatment similarly as described in Example 5. Theresults are set forth in Table 5.

                  TABLE 5                                                         ______________________________________                                                        Relative             Relative                                 Sample          sensi-               amount of                                No.    EM No.   tivity   D.sub.min.                                                                          D.sub.max.                                                                          silver coated                            ______________________________________                                        4      EM-3     100      0.03  0.50  100                                      5      EM-4     120      0.02  0.50   65                                      ______________________________________                                         Notes:-                                                                       (1) Relative sensitivity was measured at D.sub.min. + 0.10.                   (2) Relative amount of silver coated means the relative value of the          amounts of silver halide coated per unit area.                           

As apparently seen from the results shown in Table 5, the photographicemulsion according to the present invention EM-4 (Sample No. 5), ascompared with the known photographic emulsion EM-3 (Sample No. 4), isnot lowered in sensitivity in spite of decreased amounts of silver, butthere can be seen rather a substantial increase in sensitivity.

EXAMPLE 7

A pure copper bromide emulsion was prepared using the three solutionsset forth in Table 6.

                  TABLE 6                                                         ______________________________________                                        Solution J:                                                                              Acid treated gelatin                                                                             10.0   g.                                                  (isoelectric point: 7.5)                                                      KBr                59.6   g.                                                  Cu(NO.sub.3).sub.2.3H.sub.2 O                                                                    120.8  g.                                                  Distilled water added to                                                      make up 500 ml. of solution                                        Solution K:                                                                              Na.sub.2 SO.sub.3.7H.sub.2 O                                                                     31.5   g.                                                  Distilled water added to                                                      make up 250 ml. of solution                                        Solution L:                                                                              Acid treated gelatin                                                                             5.0    g.                                                  (isoelectric point: 7.5)                                                      Distilled water added to                                                      make up 500 ml. of solution                                        ______________________________________                                    

After the solution L was adjusted to pH 2.0 by addition of HNO₃ at 40°C., the solutions J and K were added by the double jet method over 40minutes to the solution L.

After completion of the addition, desalting and redispersing steps wereconducted in the same manner as in Example 3, except for maintaining thepH during the steps acidic in the range from 2 to 3 and using an acidtreated gelatin as dispersant gelatin, to prepare an emulsion containingfine copper bromide grains dispersed in gelatin.

This emulsion is hereinafter referred to as EM-5. As the result of X-raydiffraction, EM-5 was found to consist of pure copper bromide.

EXAMPLE 8

A pure copper chloride emulsion was prepared according to the sameprocedure as described in Example 7 except that 59.6 g. of KBr inSolution L was replaced with 18.64 g. of KCl. This emulsion ishereinafter referred to as EM-6. As the result of X-ray diffraction,EM-6 was found to consist of pure copper chloride.

EXAMPLE 9

Using the three solutions as shown in Table 7, there was prepared anemulsion of composite crystal wherein pure silver bromide wasepitaxially grown onto the copper bromide as prepared in Example 7.

                  TABLE 7                                                         ______________________________________                                        Solution M:                                                                             Acid treated gelatin                                                                              4.4    g.                                                 KBr                 1.0    g.                                                 EM-7 emulsion       160    ml.                                                Distilled water     840    ml.                                      Solution N:                                                                             1 M aqueous AgNO.sub.3 solution                                     Solution O:                                                                             1 M aqueous KBr solution                                            ______________________________________                                    

After the solution M was adjusted to pH 2.0 by addition of HNO₃ at 35°C., 70.6 ml. of the solution N and 70.6 ml. of the solution O weresimultaneously added over 6 minutes to the solution M. After completionof the addition, desalting and re-dispersing steps were conductedsimilarly as in Example 7.

The thus prepared emulsion is hereinafter referred to as "EM-7".

EXAMPLE 10

An emulsion of a composite crystal wherein pure silver chloride wasgrown onto copper chloride was prepared according to the same procedureas in Example 9 except that the solutions M and O shown in Table 7 werereplaced with the solutions P and Q, respectively, as shown in Table 8.This emulsion is hereinafter referred to as "EM-8".

                  TABLE 8                                                         ______________________________________                                        Solution P:                                                                             Acid treated gelatin                                                                             4.4    g.                                                  KCl                1.0    g.                                                  EM-8 emulsion      160    ml.                                                 Distilled water    840    ml.                                       Solution Q:                                                                             1 M aqueous KCl solution                                            ______________________________________                                    

EXAMPLE 11

The emulsions EM-5 and EM-6 which had not yet been chemically sensitizedwere treated similarly as in Example 5 to give samples No. 5 and No. 6.The results of sensitometry measured for these samples are shown inTable 9.

                  TABLE 9                                                         ______________________________________                                        Sample            Relative                                                    No.      EM No.   sensitivity  D.sub.min.                                                                         D.sub.max.                                ______________________________________                                        5        5        No           0.03 0.05                                      6        6        No           0.03 0.05                                      ______________________________________                                    

As apparently seen from the results shown in Table 9, EM-5 and EM-6exhibit photographic reactions very similar to EM-1.

EXAMPLE 12

Each of silver halide photographic emulsions EM-7 and EM-8 was treatedsimilarly as in Example 6. Table 10 shows the results of sensitometry ofthe samples No. 7 and No. 8 obtained.

                  TABLE 10                                                        ______________________________________                                        Sample            Relative                                                    No.      EM No.   sensitivity  D.sub.min.                                                                         D.sub.max.                                ______________________________________                                        7        7        100          0.02 0.50                                      8        8        100          0.02 0.50                                      ______________________________________                                    

We claim:
 1. A photographic gelatin silver halide emulsion comprising acomposite crystal consisting essentially of (A) (i) a solid solutioncrystal of a copper halide and a silver halide or (ii) a copper halide,as a host crystal having a mean granular diameter of at least 0.05μ, and(B) a silver halide which is epitaxially junctioned onto said hostcrystal.
 2. The photographic gelatin silver halide emulsion of claim 1wherein said host crystal is a solid solution crystal containing notless than 1 mol % of copper halide based on the total solid solutioncrystal.
 3. The photographic gelatin silver halide emulsion of claim 1or 2 wherein said host crystal contains a copper halide selected fromthe group consisting of copper iodide, copper bromide and copperchloride.
 4. The photographic gelatin silver halide emulsion of claim 1or 2 wherein said epitaxially junctioned silver halide is selected fromthe group consisting of silver chloride, silver bromide, silverchlorobromide, silver iodobromide and silver chloroiodobromide.
 5. Thephotographic gelatin silver halide emulsion of claim 4 wherein saidepitaxially junctioned silver halide is selected from the groupconsisting of silver chloride, silver bromide, silver chlorobromide,silver iodobromide and silver chloroiodobromide.
 6. The photographicgelatin silver halide emulsion of claim 3 wherein said host crystal is acopper halide.
 7. The photographic gelatin silver halide emulsion ofclaim 3 wherein said host crystal is a solid solution crystal of acopper halide and a silver halide.